Simulation Of Metal Forming Research Articles

Identification of hardening and fracture behaviors of titanium alloy by a hybrid digital image correlation and finite element method

The reliable identification of deformation and fracture behaviors of titanium alloys is essential for accurate numerical simulation in sheet metal forming, cutting process and crash. In this study, an inverse method is proposed to identify both strain hardening and fracture behavior of titanium alloys by a hybrid experimental-finite element analysis. Uniaxial and notched tensile specimens are tested on the additively manufactured and cold rolled sheet Ti6Al4V alloys. The distributions of displacement and strain on the specimen surface during the loading are measured by digital image correlation method. An identification strategy, considering the stress–strain curve, surface strain evolution and variation of specimen width, is proposed to identify the strain hardening model parameters at large strain range. Finite element simulations are performed to update the model parameters by using the iterative inverse method. The parameters of fracture model are determined through experiments on tensile specimens in combination with numerical simulation. The experimental and simulation results show the feasibility and effectiveness of the proposed identification method, that it can be further used to characterize the plastic and fracture behaviors of other metallic materials in practice.

Analysis of TRIP Steel HCT690 Deformation Behaviour for Prediction of the Deformation Process and Spring-Back of the Material via Numerical Simulation.

This paper deals with the analysis of TRIP steel HCT690 deformation behaviour. The mechanical properties and deformation characteristics of the tested material are determined using selected material tests and tests that consider the required stress states used to define the yield criterion boundary condition and subsequent deformation behaviour in the region of severe plastic deformation. The measured data are subsequently implemented in the numerical simulation of sheet metal forming, where they are used as input data for the computational process in the form of a selected material model defining the yield criterion boundary and, furthermore, the material hardening law during deformation of the material. The chosen numerical simulation process corresponds to the sheet metal forming process, including the subsequent spring-back of the material, when the force does not affect the material. Furthermore, the influence of the chosen computational model and selected process parameters on the deformation and spring-back process of the material is evaluated. In addition to that, at the end of the paper, the results from the numerical simulation are compared with experimentally produced sheet stamping.

A Review of Numerical Simulation and Modeling in High Strain Rate Deformation Processes

Numerical simulation and modeling play a crucial role in understanding and predicting the behavior of materials subjected to high strain rate deformation processes. These processes involve rapid deformation and loading rates, typically encountered in scenarios such as impact events, explosive detonations, metal forming, and crash simulations. By employing advanced computational techniques, researchers and engineers can gain insights into complex material behavior under extreme loading conditions. This paper provides an overview of numerical simulation and modeling approaches used in studying high-strain rate deformation processes. It discusses the challenges associated with capturing dynamic material response, the development of constitutive models, and the use of finite element analysis and computational fluid dynamics. The paper also highlights the importance of material characterization, model validation, and sensitivity analysis for accurate and reliable simulations. Additionally, it explores the application of numerical simulations in optimizing material properties, designing protective structures, and improving the performance of impact-resistant materials. Overall, this review paper emphasizes the significance of numerical simulation and modeling as powerful tools for advancing the understanding and design of high-strain rate deformation processes.

An overview of Methods for Simulating Sheet Metal Forming with Elastic Dies

Sheet metal forming (SMF) simulations are traditionally carried out with rigid active forming surfaces. This means that the elasticity and dynamics of presses and die structures are ignored. The only geometries of the tools included in the simulations are the active forming surfaces. One reason for this simplification is the large amount of computational power that is required to solve finite element (FE) models that incorporates elastic stamping dies. Another reason is the lack of die CAD models before the later stages of stamping projects. Research during the last couple of decades indicated potential large benefits when including elastic dies in SMF simulations. For example, for simulating die try-out or for Digital Twins of presses and dies. Even though the need and potential benefits of elastic dies in simulations are well known it is not yet implemented on a wide scale. The main obstacles have been lacking data on presses and dies, long simulation times, and no standardized implementation in SMF software. This paper presents an overview of existing methods for SMF simulations with elastic dies and discuss their respective benefits and drawbacks. The survey of methods shows that simulation models with elastic tools will be needed for detailed analyses of forming operations and also for purposes like digital twins. On the other hand, simplified and robust models can be developed for non-FEA users to carry out simple one-step compensation of tool surfaces for virtual spotting purposes. The most promising and versatile method from the literature is selected, modified, and demonstrated for industrial sized dies.

Three Industrial Cases of Sheet Metal Forming Simulations with Elastic Dies

Previous research and experience points to many advantages if sheet metal forming is simulated with elastic dies. Some areas that are enabled by simulations with elastic dies are virtual spotting, improved digital twins, and improved production support. A promising method was selected from the literature, and after important modifications it is deemed to be fast and robust for simulating industrial sized dies. The method consists of meshing die solids with a coarse mesh to represent the structural behaviour of the die. The forming surfaces are then represented by a fine shell mesh connected to the solid mesh by tied contacts with an offset. With additional modifications to reduce solver time this yields a robust and flexible way of modelling sheet metal forming with elastic dies. There is an increase in preprocessing and simulation time compared to using rigid tools, but industrial dies can now be modeled within an hour and solved within a working day. It is also easy to update the model by replacing separate parts such as die solids or forming surfaces. One of the main criteria in favor of the selected approach is the realistic modeling of blankholder and cushion systems. In this paper simulations of three industrial cases are demonstrated: one case of virtual die spotting and two cases of production support. The three cases demonstrate the importance and potential of using elastic dies during virtual die tryout, production support, and for cases like digital twins and production control.

A Homogeneous Anisotropic Hardening Model in Plane Stress State for Sheet Metal under Nonlinear Loading Paths.

In sheet metal forming, the material is usually subjected to a complex nonlinear loading process, and the anisotropic hardening behavior of the material must be considered in order to accurately predict the deformation of the sheet. In recent years, the homogeneous anisotropic hardening (HAH) model has been applied in the simulation of sheet metal forming. However, the existing HAH model is established in the second-order stress deviator space, which makes the calculation complicated and costly, especially for a plane stress problem such as sheet metal forming. In an attempt to reduce the computational cost, an HAH model in plane stress state is proposed, and called the HAH-2d model in this paper. In the HAH-2d model, both the stress vector and microstructure vector contain only three in-plane components, so the calculation is significantly simplified. The characteristics of the model under typical nonlinear loading paths are analyzed. Additionally, the feasibility of the model is verified by the stress-strain responses of DP780 and EDDQ steel sheets under different two-step uniaxial tension tests. The results show that the HAH-2d model can reasonably reflect the Bauschinger effect and the permanent softening effect in reverse loading, and the latent hardening effect in cross loading, while the predictive accuracy for cross-loading softening remains to be improved. In the future, the HAH-2d model can be further modified to describe more anisotropic hardening behaviors and applied to numerical simulations.

Modelling in materials behavior of strength differential effect and yield locus evolution with non-associated flow rule

During numerical simulation of sheet metal forming, the accurate models to describe material yielding and hardening behavior by considering the anisotropy, non-uniform evolution of the yield surface and strength differential effect are vital to predict complicated deformation and forming defects such as fracture and springback. In the present work, a novel yield model with non-associated flow rule is proposed based on the frame of S-Y2009 criterion and coupled with normal stress components and the second deviatoric stress invariants, where the former is used to describe the anisotropy and non-uniform evolution of yield loci, and the later enables the description of SD effect. Different from some other models which identify the parameters via optimization algorithms, the proposed model adopts an analytical identification method from the stress-strain curve in various loading conditions, including uniaxial tension and compression along 0°, 45°, 90° to the rolling direction, and equi-biaxial tension and compression. The flexibility of the proposed model is validated for high strength steels, aluminum alloys and titanium alloys.

Numerical simulation of sheet metal forming of an Al-Mg alloy incorporating plane strain properties in the yield criterion

In this work, numerical simulation of AA5083-O aluminum alloy sheets is carried out using Yld2000-2d yield criterion to predict thinning and variation of load with displacement in sheet metal forming. It has been found that the accuracy of predictions in numerical simulation depends on the coefficients and the stress exponent used in the yield criterion. Hydraulic bulge tests with circular and elliptical die cavities are performed to characterize the material in equi-biaxial and plane strain conditions. An improved stress exponent is determined by incorporating the material properties obtained in plane strain in the existing criterion. The improved stress exponent is validated by using it in the numerical simulations of cylindrical cup deep drawing and stretch forming at room temperature. The same exponent is also used in the numerical simulations carried out for the case of experiments conducted at 250°C. The predicted thinning and load-displacement variations from the numerical simulations are validated with the experimental measurements. A considerable improvement in the results predicted using the improved stress exponent is observed at both the temperatures.

Validation of material models for sheet metals using new test equipment

Validation is an important step after a calibration of models in order to assess their quality. In this work, new test equipment is presented that provides a comprehensive database for validation of material models for numerical analyses using FE simulation in sheet metal forming: the MUC-Test (acronym for Material Under Control). The introduced validation strategy is based on a comparison of experimental results with a numerical representation of the MUC-Test in terms of punch force and major and minor strain. The data comparison approach uses a full-field comparison over a wide range of punch stroke and thus considers the hardening behavior of the models. Extensive parameter studies are performed to investigate numerical, process and material model parameters regarding their influence on the test results. The presented validation method is applied to three materials of different material classes: The microalloyed steel HC340LA, the dual-phase steel DP590HD and the aluminum alloy AA5754. Furthermore, different material models based on the same database are compared for the DP590HD, showing the potential to identify suitable material models for specific requirements. Finally, equivalent material models based on different calibration strategies are compared. In conclusion, it is shown that the MUC-Test can be used to evaluate and compare different material models in terms of their ability to represent real material behavior in an effective and efficient way.

Characterisation of Compressive Behaviour of Low-Carbon and Third Generation Advanced High Strength Steel Sheets with Freely Movable Anti-buckling Bars

Measuring the compressive behaviour of sheet materials is an important process for understanding the material behaviour and numerical simulation of metal forming. The application of side force on both surfaces of a specimen in the thickness direction is an effective way to prevent buckling when conducting compressive tests. However, the side effects of side forces (such as the biaxial stress state and non-uniform deformation) make it difficult to interpret the measured data and derive the intrinsic compressive behaviour. It is even more difficult for materials with tension–compression asymmetry such as steels that undergo transformation-induced plasticity. In this study, a novel design for a sheet compression tester was developed with freely movable anti-buckling bars on both sides of the specimen to prevent buckling during in-plane compressive loading. Tensile and compressive tests under side force were conducted for low-carbon steel using the digital image correlation method. The raw tensile and compressive stress–strain data of the low-carbon steel showed apparent flow stress asymmetry of tension and compression, originating from the biaxial and thickness effects. A finite element method-based data correction procedure was suggested and validated for the low-carbon steel. The third generation advanced high strength steels showed intrinsic tension–compression asymmetry at room temperature whereas the asymmetry was significantly reduced at 175 °C.

Simulation of metal forming – Visualization of invisible phenomena in the digital era

The simulation of manufacturing processes has significant importance. The research and development of metal forming simulation started in the 1960s from the elastoplastic analysis of a simple plastic deformation, and it now covers a wide range of forming processes. The accuracy and applicability of metal forming simulation have significantly progressed, driven by the development of plasticity theory and numerical methods such as the remeshing technique and contact analysis algorithm. Now the targets of metal forming simulations are undergoing a transition from the macroscale analysis of deforming bodies to coupled analyses of deformations of deforming bodies and tools, and multiscale analyses of microstructure and texture. Past achievements of metal forming simulation show that it has reached the level of ‘visualizing forming phenomena’, but it will continue to evolve in the digital era, impacting the digital society and factories of the future, where machines work autonomously without human intervention. Emergent technologies require advanced materials, augmented reality, and, of course, metal forming simulation. In this paper, we reinforce the role of simulation as a means of performing computational (virtual) experiments and as a tool for the high-fidelity numerical visualization and quantification of unknown, unmeasurable, and invisible phenomena in formed components and their assembly. We will also discuss simulation–machine interactions, such as online simulation with process operation, to realize the triad of ‘process operation – data – simulation’ in the near future.

Recurrent neural network-based multiaxial plasticity model with regularization for physics-informed constraints

A recurrent neural network (RNN) based model is developed as a surrogate to predict nonlinear plastic response under multiaxial loading. The RNN-based model is trained and tested on stress versus strain curves generated using a numerical solution based on the classical radial return method. Besides simply learning the basic constitutive relationship, a novel approach is taken to enforce certain physical conditions. Specifically, regularization is employed to maintain non-negative plastic power density throughout the loading history thereby ensuring monotonically increasing plastic work and thermodynamic consistency. Enforcing physics in this manner permits coupling of the data-driven RNN approach with physics-based knowledge and laws. This has the effect of reducing the necessary amount of data and ensuring known physical laws are not violated. Since, once trained, the model need not perform the expensive task of solving nonlinear equations, its efficiency is orders of magnitude greater than its numerical counterpart. The RNN-based model has been trained on varied sets of data and the accuracy on test datasets validated. The developed model is general and robust and has widespread application such as in the simulation of metal forming, large scale plasticity, and part life prediction.

A reduced single-pattern model for the numerical simulation of multi-pattern metal forming

A reduced single-pattern model for the numerical simulation of multi-pattern metal forming

Stamped part classification and automatic dieface design

In the context of weight reduction for new car design, it is essential to downsize, or rather optimize, the Body In White (BIW) structure. A very effective approach is to take into account the influence of Manufacturing process in the performance analysis such as crash or fatigue. Further, integrating the interaction between Stamping and Crash performance should also improve the predictability of the CAE approach and lead to more efficient design. One-step simulation of sheet metal forming is a very promising technology for this application, as it can be used on the same mesh as crash analysis and can work with a simplified dieface. However, a Dieface, although simplified, must be generated for nearly all parts of the vehicle model. Hence, the implementation of product-process coupling on an industrial scale requires the development of methodologies for automatic dieface design imbedding sheet metal forming expertise. Dieface generation depends on the geometrical features of the part, but we understand the latter only if we have a framework in terms of dieface features. The authors show that such a development requires an innovative approach to stamped part classification, based both on the geometrical features of the part and on the possible strategies in dieface development. Beside its novelty, this classification has the advantage of using a decision tree based only on a vector of quantitative features, thus making it possible to implement it in automatic decision support software. An application based on a real world BiW is presented.

A Method for Simultaneous Optimization of Blank Shape and Forming Tool Geometry in Sheet Metal Forming Simulations

This paper presents a numerical method for simultaneous optimization of blank shape and forming tool geometry in three-dimensional sheet metal forming operations. The proposed iterative procedure enables the manufacturing of sheet metal products with geometry fitting within specific tolerances (surface and edge deviations less than 0.5 or 1.0 mm, respectively) that prescribe the maximum allowable deviation between the simulated and desired geometry. Moreover, the edge geometry of the product is affected by the shape of the blank and by an additional trimming phase after the forming process. The influences of sheet metal thinning, edge geometry, and springback after forming and trimming are considered throughout the blank and tool optimization process. It is demonstrated that the procedure effectively optimizes the tool and blank shape within seven iterations without unexpected convergence oscillations. Finally, the procedure thus developed is experimentally validated on an automobile product with elaborated design and geometry which prone to large springback amounts owning to complex-phase advanced high strength steel material selection.

Numerically Efficient Sheet Metal Forming Simulations in Consideration of Tool Deformation

In this study, an efficient numerical approach for automotive sheet forming simulation is proposed in consideration of deformation of tools. The proposed algorithm is based on sequential update of local contact state and pressure at the sheet metal-tool interfaces, which determines the deformation of tools. The material properties of both sheet metal and tool are determined from the standard tests, while the optimum numerical parameters such as tool mesh size are determined from numerical sensitivity analyses using 3-point bending and simplified benchmark problem. The proposed numerical approach is applied to the prediction of springback and draw-in of S-rail automotive part, which results in improved accuracy compared to the conventional rigid-body based forming simulation. Finally, in-depth analysis is provided for the deformation characteristics of a side-outer automotive part in the aspect of deformation in punch, die and blank holder. The analysis shows that tool deformation, particularly the blank holder deformation, is critical for forming quality of sheet metal parts, and the proposed method can be an efficient numerical scheme as an alternative to the conventional sheet forming simulation with rigid tool.

連載講義「入門 塑性加工シミュレーション」を始めるにあたって

連載講義「入門 塑性加工シミュレーション」を始めるにあたって

Questions process simulation of metal forming

Today, enterprises are faced with the problem of reducing the terms of design and technological preparation of production, which ultimately has a significant impact on the cost of production. In reducing time, CAD / CAM / CAE systems and CAD processes help today. In this regard, the aim of the article is to develop a model that allows you to choose the main technological equipment with a sufficient degree of reliability for hot forming processes. Research method, finite element method, which is used to analyze the stress-strain state of the forging. The results of the study are expressed in the obtained dependence, which allows you to choose the main technological equipment by weight of forgings. The conclusions obtained from the study are based on multivariate calculations by the finite element method for forgings of varying degrees of complexity, covering the most common range of crank hot stamping presses with a nominal force of 6.3 to 40 MN. The practical significance of the research results is to reduce the time of design and technological preparation of production by 15%. The proposed methodology and / or its results can be applied at enterprises engaged in the manufacture of parts by metal forming.

Effect of tension-compression testing strategy on kinematic model calibration and springback simulation of advanced high strength steels

Various studies show that application of kinematic hardening models significantly improves the accuracy of springback simulation in sheet metal forming. The springback simulation using kinematic hardening models, e.g., the Yoshida-Uemori (YU) model, is highly dependent on the testing strategy and the calibration of model parameters. In this study, the effect of tension-compression (T-C) testing strategy on calibration of YU model parameters and springback simulation of advanced high strength steels was investigated. A single-element model with T-C conditions was built in LS-OPT to determine YU model parameters on the basis of T-C tests. U-bending tests of two 980 MPa grade steels were performed to evaluate the springback prediction. Results indicate that T-C strategies, including tension-compression sequence and prestrain level show little effect on the calibrated YU model parameters as well as springback simulation of a dual phase steel DP980. However, for a TRIP-assisted high strength steel QP980, T-C strategy significantly affects both the YU model parameters and springback simulation, which is related to the complex loading-path-dependent retained austenite transformation in the QP980. A compromise strategy of T-C testing is proposed to calibrate the YU model parameters of the steel QP980, which are capable to accurately simulate its springback in U-bending.

Investigation on the Evolution of Subsequent Yield Surface of Pure Aluminum Under Changing Loading Paths Considering Microstructure Effects

The anisotropy behavior is one of the most important key issues in the simulation of sheet metal forming, which can highly affect the prediction accuracy of metal forming behavior, especially under complex loading paths. In this study, the initial and subsequent yield surfaces of the pure aluminum material are numerically investigated through the representative volume element (RVE) methodology. The crystal plasticity theory is chosen to represent the microscopic elastoplastic behavior of pure aluminum, and its polycrystalline geometrical model is built by the Voronoi algorithm. Together with user material subroutine, the initial and subsequent yield surfaces evolution of pure aluminum under different loading paths is simulated in commercial software ABAQUS/Implicit. Through the investigation, the great influence of the microtexture on the obtained inhomogeneous stress distribution of RVE model can be presented. Meanwhile, the effect of the loading directions and the predeformation is also investigated and discussed. The shape of the subsequent yield surface is also strongly dependent on both the yield definition and direction of preloading, and the high anisotropy phenomena appear corresponding to different yield definitions. At the same time, the pole figures at different forming stages are given, and the evolution of polycrystalline texture is analyzed and predicted. It can be concluded that some strong relationship between the texture evolution, the inhomogeneous stress field, and the subsequent yield surface evolution is proved and discussed. This study provides a good methodology to study the yield surface evolution of aluminum together with the crystal plasticity theory, with considering the evolution of the microtexture evolution during the plastic deformation of the metal.